This invention is directed to numerically controlled (N/C) machine tools and, more particularly, to fail-safe devices adapted to sense when N/C machine tool cutters deviate from their desired path of travel.
N/C machine tools, such as multi-spindle horizontal profilers and single-spindle vertical hydrotels, for examples, have found widespread use in a variety of fields. In general, N/C machine tools are machine tools whose cutters (or, in reverse, where the cutter is stationary, the part being cut) are program controlled, as opposed to manually controlled by an operator. In some cases, the machine tools are controlled by suitably programmed general purpose digital computers. In other cases, hard wired controllers are utilized to control the machine tools. Since the control and operation of such machines is known, it will not be discussed here in detail.
One of the problems with N/C machine tools is determining whether or not they are operating in the desired manner, i.e., whether or not they are producing parts of the right size and shape, within certain tolerance requirements. Because many parts must be machined to fine tolerances, obviously, visual observation of the part as it is being produced is inadequate to determine if these machines are operating satisfactorily. Thus, other techniques must be used. One prior art technique that is used to insure the fail-safe operation of N/C machine tools is to associate a probe with the cutter being driven. The probe is associated with the cutter in a manner such that it moves in a path of travel defined by the movement of the cutter. As the probe is thusly moved, it follows the outline of a master pattern. If the cutter deviates from its desired path of travel, the probe comes in contact with the master pattern and closes an electrical current path that, in turn, causes an electronic circuit to be activated and halts all axis motion.
While systems of the foregoing nature have found use, they have a variety of disadvantages. Because electrical probe/master pattern contact is involved, a low voltage must be present on the probe at all times. This low voltage results in operator discomfort and disconcerting spark jump. Moreover, because the probe must be cut substantially smaller (by for example 0.010 inches) than the size of the actual cutter, in order to maintain an open probe/master pattern circuit status during programmed cutter path travel, an initial undercut of the part being formed must occur before the shutdown sequence is initiated. Thus, depending upon the required tolerances, the part being cut could become unacceptable before machine operation is terminated. In addition, false probe/master pattern contact signals (known as touche' signals) are initiated by chips, high conductivity coolant and airborne particles coming between the probe and the master pattern. When such false touche' signals occur, the cutting sequence usually must return to a start point and the complete cutting cycle repeated before the part is finished. In addition, prior art devices of this nature have required that the probe and its associated slide system be solidly mounted to prevent vibration from creating false signals. However, solid mounting often results in probe damage and misalignment when an actual touche' occurs.
Therefore, it is an object of this invention to provide a fail-safe sensor system suitable for use with N/C machine tools, and the improved N/C machine tool formed by the resultant combination.
It is another object of this invention to provide a sensor system suitable for use with an N/C machine tool that does not require current to flow through a probe and a master pattern to indicate the occurrence of a touche'.
It is a further object of this invention to provide a sensor for an N/C machine tool having a probe suitable for following a master pattern at separation distances in the thousandths of an inch range.
It is also an object of this invention to provide a sensor suitable for use in an N/C machine tool that includes a mechanism for preventing chips and airborne particles from creating false touche' signals.
It is a still further object of this invention to provide a sensor suitable for use in an N/C machine tool wherein a touche' does not cause damage to the sensor.
It is yet another object of this invention to provide a sensor system suitable for use in an N/C machine tool that includes a nonelectric master pattern sensor probe and an electronic system that responds to a false touche' signal in a rapid manner.